Solvent extraction of naphthalenes



. 2,812,372 SOLVENT EXTRACTION OF NAPHTHALENES John W. Walsh, Chicago, and Le Roi E. Hutchings,

Crystal Lake, 11]., assignors to Pure Oil Company, Chicago, 111., a corporation of Ohio N Drawing. Application July 6, 1953, Serial No. 366,399

5 Claims. (Cl. 260 67 4) This invention relates to the fractionation of mixtures of petroleum hydrocarbons containing mononuclear and polynuclear aromatic compounds into a fraction richer in the polynuclear component.

, Solvent extraction, wherein is employed a liquid feed stock and a liquid extractor, is a widely used process in petroleum refining. By means of this process crude oil fractions are resolved into various classes of materials which differ from each other by their solubility characteristics. This principle permits solvent refining to be employed in the deasphalting and dewaxing of lubricating oils prepared from crude petroleum oils and also to improve their viscosity index and oxidation resistance by the removal of aromatic and naphthenic constituents, an effect which also reduces the carbon and sludge-forming tendencies of these lubricating oils. Extraction with selective solvents has also been employed for the desulfurization of light petroleum distillates where the concomitant removal of aromatic hydrocarbons from the distillate is not disad vantageous.

p The petroleum industry has also been instrumental in the development of a versatile chemical industry which has created a need for a wide variety of raw materials, including various hydrocarbons. Petroleum being a complex' homogeneous mixture of a very large number of hydrocarbons plus a small quantity of other materials is an excellent source for hydrocarbons which are to be employed as raw materials and subjected to further processing. However, the separation of relatively pure hydrocarbons or concentrated solutions thereof from petroleum is adiificult task. While fractionationof petroleum mixtures may be effected by distillation, adsorption, absorption, crystallization, and so forth, because of the satisfactory experience in operating the above mentioned solvent refining processes, the petroleum industry has utilized to a' great extent the principles of solvent extraction in the recovery of hydrocarbons which are difficult to separate in other types of fractionating processes. In spite of the effectiveness of solvent refining processes as a means for separating hydrocarbon components which have substantially the same volatility, this technique is generally limited to the separation of aliphatic hydrocarbons from cyclic hydrocarbons, or even in the separation of more unsaturated aliphatic hydrocarbons frornless saturated aliphatic hydrocarbons. Fractionation of these components by solvent extraction can be carried out rather readily becauseof the solubility characteristics of the component hydrocarbons involved in relation to the selective solvent employed. The separation of mixtures of aromatic hydrocarbons, however, presents a more difiicult problem. Experience has shown that the conventional techniques of distillation, crystallization, and the like are not satisfactory forseparating mixtures of mononuclear and polynuclear aromatic hydrocarbons into fractions richer in the polynuclear components. Similarly solvent extraction processes have not been generally employed in this capacity because of their low efiiciency. According to this invention, however, it has been found that the principles of 2,812,372 Patented Nov. 5, 1 957 solvent refining may be used advantageously to effect this separation.

It is therefore an object of this invention to provide a solvent extraction process which may be employed in the separation of polynuclear aromatic hydrocarbons from admixture with mononuclear aromatic hydrocarbons. It is a more specific objective of this invention to employ the principles of solvent extraction to separate mixtures of naphthalene and alkyl derivatives thereof, and benzene and its alkyl derivatives into a fraction enriched in naphthalene and its alkyl derivatives.

It is well known that aromatic hydrocarbons are more powerful solvents than aliphatichydrocarbons. Inasmuch as the mechanism of solvent extraction is based upon the miscibility of the solvent in the solution to be extracted, the high solvency powers of aromatic hydrocarbons have prevented general acceptance of solvent extraction in the separation and recovery of aromatic hydrocarbon mixtures. The problem of miscibility of the solvent in the solution is illustrated by Table I which lists a plurality of conventional selective solvents which are completely miscible in mixtures of aromatic hydrocarbons.

TABLE I S02 Acetonitrile Triethylene glycol and acetonitrile Furfural Dichloroethyl ether Ethylene glylcol diethyl ether Ethylene glycol monoethyl ether Dichloroethyl ether-hexane Nitromethane Methylacetoacetate Dimethoxy tetraglyc-ol Even in the event that immiscible solvents can'be obtained, the refiner is faced with the additional problem of inoperativeness of the solvent refining process to effect the separation of aromatic hydrocarbon mixtures. For example, the inoperativeness of solvents conventionally used in the separation of aliphatic hydrocarbons from aromatic hydrocarbons is demonstrated by the data in Table II.

TABLE II Separation of naphthalenes from alkylated benzenes by solvent extraction Composition of Hydrocarbon- Phase of Extract Obtained Qompo- Using Extracting Solvents 1 sition of Components Original Mixture Plropy- Polyethylene Glycol one Glycol Naphthalene, percent 7. 1 7.1 5. 6 5. 3 5. 6 l-Me-Naphthalene, percent 21. 3 24. 9 22. 2 24. l 22v 0 2Me-Naphthalene, p 7

cent 33. 9 37. 8 36. 4 37. 9 36. 1 Alkyl Benzenes, percent. 37. 7 30. 2 35. 8 32. 7 36. 3 Yield of Material Extracted, Vol. percent ,3 44. 5 49. 0 63. 0

1 Solvent to hydrocarbon ratio 1:1.

However, according to this invention, it has been found that the condensation products prepared by reacting the monoethanoid nitrile, acrylonitrile, with either water, hydrogen sulfide or ammonia in the presence of a suitable condensation catalyst may satisfactorily be employed in the separation of hydrocarbon mixtures containing mono nuclear and polynuclear aromatic hydrocarbons topro duce'. a. fraction enriched in .the polynuclear constituent.-

P, W A.

3 Specific. examples. of. such. condensation products. whichv may be used as solvents in the instant invention are more In Efltctivenms t, this, and: iim'hvdipropioni'triles as selective solvents !or mzp'htha'l'ens Solvent" Nrrphthai- Yield, 1 Percent Solvent Ratio- Phase lenesflol. 5 Volt, Enrich- Percent. Percent ment 1:1 Extract, 62.3, 25 V 48 It is thus seen that the solvent extraction process of this invention has the ability to extract naphthalenes from benzenes, a system very difiicult to process by means of solvent extraction. In general, the solvents employed in the instant invention were able. to effect a concentration of the naphthalenes in the extract phase by enriching the naphthalene concentration from 42% to 60% in a single stage extraction, each of the solvents employed evincing substantially equivalent selectivity. Although the sub-v stantial equivalency of each solvent,with regard to. selectivity, is shown, consideration of the process conditions may make it more desirable to use the oxy-derivau tive because of its physical properties. In the use of this particular composition, the recovery of the enriched aromatic hydrocarbon mixture and solvent from the extract phase is facilitated because the use. of steam distillation may be expeditiously employed to recover the aromatic hydrocarbons separated in the extract phase. With the separation of the aromatic hydrocarbons there results the production of a water-rich phase and a solventrich. phase. Upou'cooling, these phases. can be readily separated, the water-rich phase being recycled to the steam distillation step and the solvent-rich phase being recycled for further use in the extraction step of the process. The iminoand thin-derivatives, however, can not be employed as effectively in this manner, inasmuch as the. recovery of the imino compound is complicated due to its complete miscibility with water at normal temperatures. Although the thin compound is not completely miscible with water at the temperature, at which a, normal steam distillation step would be carried out, elevated pressures would be necessary to effect an efiicient separation of aromatics from the solvent by steam distillation.

It may also be desirable to carry out the solvent refining process of this invention by adding small amounts of water to the selective solvents employed therein. It-has been found that the efficacy of this extraction process may be enhanced by carrying out the process employing solvents containing small amounts of water. The amount of water employed will depend upon the solvent em efiect'is shown in Table IV'fin which is compiled the re sultsof. extracting. a. mixture containing. 38% ot alkyl benzenes and 62% of naphthalene and alkyl derivatives thereof in a single stage extraction process employing fi,;8-oxydipropionitrile as the selective solvent. In one instance a substantially anhydrous solvent was used, while the other illustrative extraction was carried out using a solvent containing. 1% by volume of water.

TABLE IV Separation of naphthalenes from benzenes employing fi,fi'-0xydipr0pi0nitrile Run N 1 2 Water Content oi Solvent, V01. Percent 0.0 1. 0 Solvent-Hydrocarbon Ratio 1:1 1:1 Composition of Extract:

Alkyl Benzenes 25.1 20.7

Naphthalenes 74. 9 79,3

Although the foregoing data illustrating the several features of the instant invention were obtained; emp1oying a single stage extraction, it is to be understood that the. foregoing examples were presented merely as illustrative and non-limiting demonstrations of the instant in vention. The solvent extraction process of this invention may be carried out employing several countercurrent extraction stages to improve the separation. In addition, the solvent to hydrocarbon feed ratio may be varied from that employed in the illustrative examples. Inasmuch as the solvents employed in this invention are not sensitive.

to temperature and their efficiency is not appreciably af-.

fected thereby, the process may. be operated over a relatively broad temperature range, although preferably at atmospheric temperature. Similarly, other modifications. of conventional solvent refining techniques may be employed in carrying out the instant invention and are to be considered within the scope of the invention described. in the appended claims.

What is claimed is:

1. A process for separating a polymer mixture-Uproduced in a conventional hydroforming process consisting: essentially of naphthalene and alkyl derivatives thereof and alkyl benzenes into an extract fraction enriched in the naphthalene constituents which comprises solvent extracting the hydrocarbon mixture with a solvent consisting of a dialkylnitrilederivative selected from the group consisting of p,fi-thiodipropionitrile, fl,[:?'-oxydipropiorecover therefrom said fraction enriched in the naphthalene constituents, separating the remaining mixture of ,6,18'oxydipropionitrile and water into a water phase and a solvent phase, separating the solvent phase and recycling it to be .further employed in said solvent extracting.

3. A process for separating a polymer mixture pro: duced in a conventional hydroforming process consisting essentially of naphthalene and alkyl derivatives thereof, and alkyl benzenes into an extract fraction enriched in the naphthalene aromatic constituents which comprises solvent extracting the hydrocarbon mixture with :a solvent consisting of an admixture of. a dialkylnitrile derivative selected from the group consisting of p,p'-thiodipropionitrile, B,,9'- oxydiprofiionitrile and B,B'-iminodipropionitrile, and 15 vol. percent of water and recovering the fraction of the hydrocarbon mixture enriched in the polynuclear constituents in the extract phase.

4. A process in accordance with claim 3 in which a solventzhydrocarbon mixture ratio of 1:1 is employed.

5. A process in accordance with claim 4 in which said solvent consists of an admixture of fl,p'-oxydipropionitrile and 1-2 vol. percent of water.

References Cited in the file of patent UNITED STATES PATENTS OTHER REFERENCES Medcalf et al.: Petroleum Refiner, vol. 30, July 1951, pp. 97-100. 

1. A PROCESS FOR SEPARATING A POLYMER MIXTURE PROP DUCED IN A CONVENTIONAL HYDROFORMING PROCESS CONSISTING ESSENTIALLY OF NAPHTHALENE AND ALKYL DERIVATIVES THEREOF AND ALKYL BENZENES INTO AN EXTRACT FRACTION ENRICHED IS THE NAPHTHALENE CONSTITUENTS WHICH COMPRISES SOLVENT EX-NSISTTRACTING THE HYDROCARBON MIXTURE WITH A SOLVENT CONSISTING OF A DIALKYLNITRILE DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF B,B''-THIODIPROPIONITRILE, B,B''-OXYDIPROPIONITRILE, B,B''-IMINODIPROPIONITRILE, AND A WATER-CONTAINING MIXTURE THEREOF CONTAINING 1-5 VOL, PERCENT OF WATER, AND RECOVERING A FRACTION OF THE POLYMER MIXTURE EN-RICHED IN THE NAPHTHALENE CONSTITUENTS IN THE EXTRACT PHASE. 